(1) Field of the Invention
The present invention relates to a surface tensiometer and a surface tension measuring method and also to a concentration controlling device and method utilizing the surface tensiometer and the surface tension measuring method, and more paticularly to a device or method of measuring or controlling concentraion of a liquid by measuring the concentration as a surface tension of the liquid, the device and the method being used for e.g. measuring alcohol concentration of a fountain solution used in an offset printing machine or a concentration of other kinds of water solution.
(2) Description of the Prior Art
A device for controlling concentration of fountain solution (alcohol water solution) for use in e.g. an offset printing machine is known from a prior-art reference U.S. Pat. No. 3,848,618.
The device of this reference invention essentially comprises a U-tube formed by connecting lower portions of two cylinders with a narrow pipe, with one of the cylinders being preliminarily filled with a reference water solution and the other cylinder being gradually and continuously filled with the fountain solution. The surface of the reference water solution is vertically moved in accordance with a specific gravity of the fountain solution. Further, the cylinder containing the reference solution attaches at a predetermined position thereof an electrode for detecting the surface of the reference water solution. Thus, by detecting the surface of the reference water solution by this electrode, a difference between the specific gravities of the fountain solution and the reference solution is measured, which measured difference is utilized consequently for controlling alcohol concentration of the fountain solution.
However, with the above device, since the control-object fountain solution need be continuously fed into the cylinder, there occurs the problem of considerable soiling of the U-tube or the electrode by contaminant present in the fountain solution in direct proportion to the feeding amount of the control-object solution. Further, since the liquid surface of the reference water is not sufficiently stabilized, this prior-art device is incapable of accurate measurement of the specific gravity of control-object solution. Moreover, the device has the disadvantage of its complicated construction which makes its cleaning operation difficult.
In view of the above-described state of the art, the primary object of the present invention is to provide a device and a method for readily, reliably and accurately measuring a surface tension of a liquid, the device and method eliminating the necessity of continuous feeding of the liquid.
A further object of the present invention is to provide a device and a method for controlling concentration of a liquid which surface tension value varies in proportion to its concentration.